1. The Field of the Invention
The present invention relates generally to systems and methods for analyzing samples or specimens. In particular, the invention relates to systems and methods for detecting the unintentional use of short and long samples in the analyses of sample, specimen, or assay fluids.
2. The Relevant Technology
One important physiological test that is frequently performed by medical and veterinary professionals is the detection and quantification of chemical analytes in biological samples or specimens. Biological samples or specimens that can be tested include a variety of biological fluids, such as blood, plasma, urine, sputum, semen, saliva, ocular lens fluid, cerebral fluid, spinal fluid, and amniotic fluid. Of course, other fluids can be similarly tested for analyte presence and concentration, including tissue culture media, food and industrial chemicals, and environmental samples.
Such biological tests of blood plasma and other biological fluids typically require that a sample or specimen be inserted into a clinical analyzer. The biological samples or specimens are typically processed with various intermediate steps before testing, such as mixing with a diluent. Such clinical analyzers are often capable of quantitatively analyzing a variety of different analytes from a single sample or specimen.
One such clinical analyzer utilizes a rotor, which divides fluids into predetermined volumes for analysis in a variety of optical tests or assays. These analyzers are designed to measure volumes of a biological fluid, such as blood, remove cellular components, and mix the fluid with an appropriate diluent for analysis, for example by spectrophotometric testing. Typically, the rotors provide a plurality of discrete volumes of sample or specimen in separate cuvettes in which the sample or specimen is optically analyzed. One such centrifugal rotor is disclosed in U.S. Pat. No. 6,235,531 to Kopf-Sill et al., incorporated herein by reference.
Although clinical analyzers typically dilute the sample or specimen very precisely, both human and machine error can occur, thus providing false readings. In particular, in the measurement of clinical chemistries a phenomenon called “short sample” is a source of very damaging errors. A “short sample” is very difficult to detect, but can have devastating consequences in the diagnosis of illnesses or monitoring of recovery. For example, under some circumstances the dilution is much larger than a nominal one, resulting in measured values proportionally smaller. This is called a “short sample.” The cause of this is usually the failure of the equipment or the operator to provide the precise amount of sample or specimen expected by the instruments performing the measurements. Thus, the analytical data will include inaccurately low numbers. Similarly, a low dilution will result in a high concentration of sample or specimen resulting in a “long sample” that provides inaccurately high numbers.
Currently there are no reliable and simple methods to detect the presence of such short or long samples. The only tools available are based on physiology, because for some analytes the body controls the concentration within a relatively narrow window. Measured values below that physiology window are used as indicators of a possible short sample. One example of such a current method is the subjective opinion of a user analyzing the results, who may recognize that a test value falls below or above the standard range. The user may then order a repeat test. However, it is apparent that this method is very imprecise and extremely subjective. Accordingly, there is a need for improved methods and systems to detect the presence of short and long samples.